The suspension system of a vehicle is primarily provided to isolate the occupant compartment from road irregularities. However, suspension also plays an important role in reducing the amount of energy expended as the vehicle encounters bumps in its path. The most common approach to vehicle suspension is to provide an articulating linkage that allows the tire, wheel, brake assembly, bearing arrangement and associated structural member to move independently, but in a predetermined manner relative to the main vehicle structure. The subassembly of tire, wheel, brake assembly, bearing arrangement and associated structure is generally referred to as the unsprung mass while the main vehicle structure, including the occupant compartment is termed the sprung mass. When the vehicle encounters a bump the articulating linkage allows the unsprung mass to move up and over it. A spring is provided to store the imparted energy which is used to restore the unsprung mass to its predisturbed state. It is also common practice to provide a damper or shock absorber to control the oscillatory nature of the spring-mass system so that it is expeditiously brought to rest. In this way the vehicle can be simply considered a five mass system consisting of a single, large sprung mass (1) and four independent unsprung masses (3) as shown schematically in FIG. 1.
The motion of each unsprung mass is determined by the geometry of the associated articulated linkage that connects the unsprung mass structural member to the main vehicle structure. A combination of independent links and appropriately restrained connection joints results in an overall system motion that is generally limited to being fully controlled by the spring and damper. The most common articulated linkages associated with independent unsprung mass suspension systems can be categorized as double ‘A’ arm (FIG. 2), MacPherson strut (FIG. 3) and multi-link (FIG. 4).
The double ‘A’ arm configuration illustrated schematically in FIG. 2 consists of a relatively simple four bar link arrangement made up of the main vehicle structure (1) (not shown in FIG. 2), an upper control arm (10), a lower control arm (11) and a structural member or upright (12) that is adapted to carry all of the unsprung mass components such as the tire, wheel, brake assembly and bearing arrangement. Each of the connection joints is configured to constrain all but a single rotary degree of freedom which results in a single translational degree of freedom motion of the upright (12) that is in turn controlled by a coil spring (13) and conventional hydraulic damper (14). Additional complexity is typically introduced with the use of multiple degree of freedom compliance at each joint in the interest of adding additional isolation to the main vehicle structure (1). These compliances are typically provided by rubber bushings that return spring stiffness and damping in all three translational degrees of freedom. The stiffness of these rubber bushings is typically very high in comparison to that of the coil spring (13).
FIG. 3 schematically illustrates a MacPherson strut arrangement that consists of a lower control arm (22), a structural member or upright (23) that is adapted to carry all of the unsprung mass components such as the tire, wheel, brake assembly and bearing arrangement and a strut (24) that is rigidly attached to the upright and provides a linear motion control as well as containing a conventional hydraulic damper. The lower control arm joints are configured to constrain all but a single rotary degree of freedom while the upper strut mount releases two rotary degrees of freedom. This configuration results in a single translational degree of freedom motion of the upright (23) that is in turn controlled by a coil spring (25) and the conventional hydraulic damper within the strut (24).
The multi-link suspension configuration illustrated schematically in FIG. 4 is only one of many different available arrangements. Although in many cases these multi-link configurations closely approximate the motion of a four bar link, more complex kinematics are available allowing the upright (33) to provide self-steering and non-linear movement which is deemed necessary for advanced vehicle dynamic behavior. It is also common for multi-link configurations to be kinematically over-constrained, or locked, with only the rubber bushing compliances allowing the required freedom of motion.
All of the conventional articulated linkages described above possess numerous inherent limitations that include significant complexity, the requirement for substantial and extensive vehicle structure for mounting, considerable cost and a requirement for large packaging volumes to contain their motion. There have been a number of prior art attempts to address these limitations. U.S. Pat. No. 3,578,354 describes a form of vehicle suspension system in which the commonly utilized articulated linkages have been replaced by a hub housing and a pair of radially extending pins that allow slideable movement of the wheel along an axis perpendicular to the spindle axis. The radially extending pins pass through frame supporting arms that are rigidly connected to the main vehicle structure and contain a pair of integrated bushings that allow the desired slideable movement but constrain all other degrees of freedom, with the exception of rotary steering motion if desired. A coil spring is introduced on one of the radially extending pins to absorb shock loads. In this manner the suspension system of U.S. Pat. No. 3,578,354 eliminates all conventional articulating links and their associated packaging volume. The entire suspension motion is contained within the wheel, thereby liberating a significant amount of the vehicle volume for alternative use. The mounting of the frame supporting arms has far more freedom than the connection of conventional articulating links so that structural optimization would be far more effective.
Although this prior art embodiment describes a novel approach to simplifying the suspension system of a vehicle, it does not provide any method of damping the spring motion. Additionally, detailed calculation and a study of existing road vehicle suspension springs illustrate that the spring size and package suggested in U.S. Pat. No. 3,578,354 are unrealistically small. A correctly sized spring would not be capable of fitting in the space provided by this prior art configuration. Finally, this prior art suspension configuration describes an integral tie bar joined to the hub housing that allows the attachment of a steering arm adapted to provide steering of the vehicle. Because the hub housing is configured to move in a predominantly vertical and linear manner and the steering arm would describe an arc from its inner end, a self-steering motion would occur during suspension movement. This form of self-steering phenomenon is generally referred to as toe-steer or bump-steer and is a highly undesirable characteristic that could not be eliminated using the structure described in U.S. Pat. No. 3,578,354.
Some of the limitations of U.S. Pat. No. 3,578,354 are overcome in the prior art configuration claimed in U.S. Pat. No. 6,113,119 which similarly describes a wheel connecting assembly for an automobile comprising a hub, a wheel, a wheel carrier, a support comprising a guide member for guiding the wheel carrier in translational movement relative to the support and a mounting means for mounting the support on the chassis of a vehicle. In a similar manner to U.S. Pat. No. 3,578,354, all of these components are accommodated in a limiting envelope within the wheel of the vehicle. A means for supporting the automobile load transmitted by the support to the wheel carrier is provided which is also contained within the limiting envelope. This supporting means is described as a coil spring but is illustrated to be of a more realistic size and configuration than shown in U.S. Pat. No. 3,578,354. However, the coil spring is packaged at a large offset to the translational motion axis defined by the guide member. This large offset would introduce highly undesirable torque loads to the guide member resulting in friction within the suspension movement that is known by those skilled in the art to seriously degrade performance.
Although this prior art embodiment describes an assembly that allows all the essential function of the suspension to be integrated into the actual interior of the volume within the wheel with a realistic spring package and a method for eliminating bump-steer, it does not provide a conventional damper to control the oscillatory nature of the spring-mass system. Dampers or shock-absorbers as used by the automotive industry are almost exclusively of a hydro-dynamic configuration where a controlling force is generated in response to suspension velocity via some form of variable orifice flow. U.S. Pat. No. 6,113,119 makes reference to electromechanical means to control the deflecting movements of the wheel as an alternative to the spring and damper, but as this method has no current application in the industry, the lack of inclusion of a conventional damper is a significant limitation of this prior art arrangement. Both the steering arrangement and spring position would impart significant frictional loads in the suspension movement which is highly undesirable.
U.S. Pat. No. 6,357,770 describes an “in-wheel suspension” system that permits all or most of the moving suspension components to be mounted within the volume enclosed by the rim of the wheel. The improvement over the prior art described above is that a spring and damping mechanism are included so that fully controlled suspension motion would be possible. The described wheel suspension comprises a hub mounting assembly which comprises a hub/bearing assembly including an axle and bearings. The hub mounting assembly is mounted and connected to a suspension frame by a motion-controlling inter-engaging sliding mount assembly which permits the hub plate to slideably move in a controlled manner. The inter-engaging sliding mount assembly permits motion of the hub plate with one degree of freedom. A spring mechanism is mounted extending between, and connecting to both, the hub plate and the suspension frame and preferably includes a damping device. In this manner a similar motion to the previously described prior art is achieved without the requirement of an articulated linkage and the system includes an integrated spring-damper and can be mounted substantially within the volume of a wheel rim. However, once again, detailed calculation and a study of existing road vehicle suspension springs illustrate that the spring and damper size suggested in U.S. Pat. No. 6,357,770 are unrealistically small. In fact, this prior art description self-professes to be only applicable for light road vehicles such as electric vehicles, human powered vehicles, solar powered vehicles and the like. The configuration would not be suitable for general purpose road going vehicles due to the light duty nature of the inter-engaging sliding mount assembly and the small size of the spring mechanism and damping device. Additionally, this prior art configuration does not describe a methodology for allowing the moving suspension components to be steered which is a significant limitation of this arrangement.